(a) Field of the Invention
The present invention relates to an eight-speed automatic transmission. More particularly, the present invention relates to an eight-speed automatic transmission that combines a plurality of planetary gear sets, and a first clutch and a third clutch thereof are disposed between a compound planetary gear set and an output shaft so that a lubrication structure thereof can be simplified.
(b) Description of the Related Art
A typical shift mechanism of an automatic transmission utilizes a combination of a plurality of planetary gear sets. A powertrain of such an automatic transmission changes rotating speed and torque received from a torque converter of the automatic transmission and transmits the changed torque to an output shaft.
It is well known that when a transmission realizes a greater number of shift speeds, speed ratios of the transmission can be more optimally designed and therefore a vehicle can have better fuel mileage and better performance. For that reason, an automatic transmission that enables more shift speeds is under constant investigation.
In addition, with the same number of speeds, features of a powertrain such as durability, efficiency in power transmission, and size depend a lot on the layout of combined planetary gear sets. Therefore, designs for a combining structure of a powertrain are also under constant investigation.
A manual transmission that has too many shift-speeds causes inconvenience of excessively frequent shifting operations to a driver. Therefore, the positive features of more shift speeds are more important for automatic transmissions because an automatic transmission automatically controls shifting operations basically without needing manual operation.
In addition to various developments regarding four and five speed powertrains, an eight speed automatic transmission has recently been developed.
In the eight-speed automatic transmission, an arrangement of friction elements, such as brakes and clutches, may influence design of a lubrication structure and may determine the total size and weight of an automatic transmission.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.